Power modulation for radiotransmission



R. A. HEISING. POWER MODULATION FOB RADIO TRANSMISSION.

APPLICATION FILED SEPT. 21-19I5.

. 1 383,807; Patented July 5, 1921.

W/fn ealses:

D7 v e'ni'or RAYMOND A. HEISING, OF EAST ORANGE, NEW JERSEY, ASSIGNOR,BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A COR-DURATION OF NEW YORK.

POWER MODULATION FOR'RADIOTRANSMISSION.

ssasor.

Patented July 5, 1921.

Application filed September 21, 1915. Serial No. 51,762.

To all whom it may concern:

Be it known that I, RAYMOND A. IIEISING, a citizen of the United States,residing at East Orange, in the county of Essex and State of New Jersey,have invented certain new and useful Improvements in Power Modulationfor Radiotransmission, of which the following is a full, clear, conclse,and exact description. I

This invention relates to theuse of highfrequency currents in radiosignaling, and particularly to the use of these currents for radiotelephony. The object of thisinvention is to provide means formodulating the high-frequency power used in wirelesstelephony ortelegraphy in accordance w1th the thisresult without requiring thepassage of' heavy currents directly through the tele phone transmitteror other signaling device.

In this invention it is proposed to secure the modulation of the totalhigh-frequency power by varying the impedance of a vacuum tube placed inthe antenna circuit. It has been found that thermionic vacuum tubes,particularly of the audion type, are well adapted for this purposebecause 0 their relatively high impedance, and because of the fact thatthis impedance can be varied by means ofa signaling device, inparticular a telephone transmitter, which is required to handle only alimited amount of power.-

In general, however, a thermionic device is unilateral, and, in order topermit the passage of both halves of the high-frequency oscillations, itis necessary to make the system symmetrical by usingtwo such thermionicimpedances suitably connected, or by using a specially constructedimpedance of this character which is symmetrical. The invention will bebest understood by reference to the following specification:

Referring to the drawings, Figure 1 shows a transmitting stationimrorporating the invention; Fig. 2 shows a modification of F 1g. 1;Fig. 3 shows a further modification. In these figures, 1 represents anysuitable high: frequency generator of large power, such as is necessaryfor radio signaling. This generator is inductively connected by means ofthe transformer 6 to the antenna 7 which may be the usual elevatedconductor, or any other suitable radiating system or energy transmittingor translating element.

In Fig. 1, there is shown in series with the Y secondary of thetransformer 6 a thermionic amplifier 10 of the audion type having theusual heated element 12, grid 13 and plate 14k, the output circuit 12, 11 of the amplifier being connected to the antenna circuit. In parallelto this thermionic amplifier 10, is placed a similar amplifier 11 whichhas similar electrodes 15, 1.6 and 17. This amplifier 11, however, isconnected in the reverse direction to 10. This reversal of direction isfor the purpose of rendering the antenna system bilateral, in order thatoscillations may take place in either direction, well known, positivecurrent can flow only from the plate 14 to the filament 12, or from theplate 17 to the filament 15. .lonnected to the input circuit of theamplifier 10 is the tenna, is grounded in the usual manner at 18.

The operation of the system is as follows: High-frequency oscillationsof uniform amplitude are generated by the generator 4,

and are impressed upon the radiating antenna. The amplitude of theseoscillations is determined by the impedance or effective resistance ofthis antenna. If this impedance is varied or modulated in accordancewith signals, the oscillations will be similarly modulated. Whensignals, or control impulses, are impressed upon the microphone 24,low-frequency currents of low power are impressed upon the inputcircuits of 10 and 11 by means of the three-winding transformer 20, 21,22. The changes in the potentials of the grids 13 and 16 bring about arelatively large change in the impedance of these thermionic amplifiers,and accordingly the oscillations in the radiating system are modulatedin the same manner.

Fig. 2 shows a modification in which the two amplifiers of Fig. 1 arecombined in a single tube. In this case the plates 1.4 and 17 areunnecessary, and accordingly the thermonic impedance comprises merely afor, as is tube inclosing the heated electrodes 31 and 32, and the grids33 and 34. In view of the fact that both 31 and 32 are heated elements,this device is bilateral, that is, current may flow in either direction.A threecoil transformer 40, 41 and 42 with, microphone 44 and battery 43is connected to the input circuits in precisely the same manner as shownin connection with Fig. 1.

In view of the fact that theseimpedances shown have a very largeresistance, there results the introduction of a large resistance intothe antenna. A circuit arrangement by which this dilficulty is overcomeis shown in Fig. 3. A winding of a transformer is introduced into theantenna circuit, and'the secondary of this transformer, consisting of alarge number of turns, is connected by a circuit including a variablecondenser 51 to such a modulating device as is shown in Fig. 2. It isobvious that in place of this modulating device the one shown in Fig. 1

' may be used in the arrangement of Fig: 3.

In using this transformer 50, the apparent resistance introduced intothe antenna may be made ofany desired value.

In general, the antenna is tuned to the sending frequency, which is thefrequency .of the generator 4 and the value of the current flowing inthe antenna circuit will depend only upon the voltage impressed and thesum of the resistance of the antenna, the coil and the resistanceintroduced by the tubes.

the effective reslstance in the antenna circuit, which variation is dueto the variations of the tubes. For complete modulation it is,therefore, necessary that the resistance introduced by the tubes belarge enough to reduce the highv frequency current in this circuitto'zero when the low frequency input to the modulating device has itsmaxi-- mum negative val u e. It is also necessary for efficiency thatthe resistance of the tubes become very small when the low frequencyoutput has its maximum positive value.

By complete modulation, as used above,

is such modulation that the maximum negative value of the low frequencyinput shall just reduce the modulated high frequency oscillations tozero amplitude. In this case the high frequency oscillations are justlarge enough to 'carry the maximum of the low frequency oscillations. luother words, the picture of the low frequency oscillations, as shown inthe envelop of the high frequency oscillations, just comes down to thezero line, having none of the picture cut off by this zero line, and, onthe other hand. leaving none of the high frequency between the envelopand the zero line unused.

It is important that the transformers 20, 21 and 22 be so connected thatboth grids are at all times of the same sign with rcga rd In all themodifications shown, the. modulation is produced by the variation of totheir respective filaments. When this sign is positive, the flow ofelectrons from filament to the corresponding to a decreased resistanceof the tube to current in this direction. Current cannot, however, flowin the opposite direction in the tube. onsidering a half cycle of thehigh frequency in which the antenna is positive with respect to theground, it is apparent that the current will, duringthis time,fiowthrough the tube 11 but not through the tube 10. When the antenna isnegative with respect to the ground, current will flow through the tube10 but not through the tube 11. The action of the positive part of thelow frequency cycle being to make the grids positive with respect to thefilament in both tubes, the high frequency currents will flow readilythrough the circuit which offers a low resistance to it. hen, however,the grids are made negative with respect to the fila-' ments, thecurrent will be impeded in both tubes, giving the effect of an increasedresistance in the antenna circuit. It is thus evident that the devicewill modulate the high frequency oscillations, and it is further evidentthat in order that both half cycles of the high frequency may be treatedalike, it is necessary that the tubes 10 and 11 have the sameconstants.In the case of Fig. 2, the modulation is again effected by theintroduction of a proper impedance in the antenna circuit. In this case,as well as in the other. it is necessary that the grids both take thesame sign with regard to their respective filaments.

Although this invention has been described as being particularly adaptedfor wireless telephony, it is to be understood that it may be usedequally well in, radio signaling of any kind or in ordinary telephony orwire signaling. In the ease of wire signaling the antenna is replaced bythe usual transmission circuit.

lVhat is claimed is:

1. A source of substantially constant high frequency electromotiveforce, a circuit upon which substantially all of said electromotiveforce is impressed, a modulator comprisin two constantly operativeasymmetric conducting devices connected in opposition in said circuit,signaling means controlling'said devices. substantially all of thecurrent induced in said circuit by said electromotive force passingthrough said devices and means for transmitting the energy of saidinduced current.

2. In a wireless signaling system, a gem erator of high frequency highpower oscillations, a radiating antenna connected therewith, twoconstantly active unilateral impedanccs cowluctively connected inreplate will be made easier,

source of low frequency variations and means whereby said impedances aresimilarly controlled by said low frequency va-' riations.

3. In a wireless signaling system, a generator of high-frequency,high-power oscillations; a radiating antenna inductively connectedtherewith; two constantly active thermionic amplifiers of the audiontype connected in reverse directions in said antenna and in parallel toeach other and means for similarly modulating the impedance of saidamplifiers in accordance with signalsto be transmitted.

4. In a wireless signaling system, a generator of high-frequency,high-power oscil-. lations; a radiating antenna inductively connectedtherewith; two constantly active thermionic amplifiers of the audion,type connected in reverse directions in said antenna and in parallel toeach other and a telephone transmitter assoc'ated with said amplifiers,for modulating the oscillations .in said antenna in accordance withsignals to be transmitted. i I

5. In =,a wireless signaling system, a generator of high-frequency,high-power oscillations; a radiating antenna inductively connectedtherewith; two thermionic amplifiers of the audion type, connected in"reverse directions in said antenna by means of the output electrodesand connected in parallel to each other a circuit containing a batteryand a telephone transmitter, said circuit being inductively connected tothe input circuits of the amplifiers, whereby the impedance f theantenna is varied in accordance with the signals to be transmitted.

6. In a wireless signaling system, a generator of high frequency highpower oscillations, a radiating antenna connected there-. with, ingconstantly active sources of electronstreams, said conductors beingconductiv'ely. connected in reverse directions tosaid antenna and inparallel with each other, and means for impressing upon said sourcessimilar variations in accordance with the signals to be transmitted.

7. In a wireless signaling system, a generator of high frequency highpower oscillations, a radiating antenna connected therewith, constantlyactive thermionic impedances connected in reversedirections in saidantenna and in parallel to each other, and means for impressing lowfrequency variations of similar phase upon said impedances, whereby theimpedance of said antenna is varied in accordance with said lowfrequency variations.

8. In a wireless signaling system, a generator of high frequency highpower oscillations, a radiating antenna connected therewith, twoconstantly active thermionic impedanccs connected in reverse directionsin two asymmetric conductors compris said antenna by means of the outputelectrodes and connected in parallel to each other a source of lowfrequency variations adaptedto impress oscillations of similar phaseupon said impedances, whereby the impedance of said antenna is varied inac cordance with said low frequency variations. r

9. An antenna, two constantly active ther-' mionic inipedances connectedin parallel in reverse directions between two points in and means forvarying each.

said antenna,

impedance 'inaccordance with signals.

10. A circuit, two constantly active asymmetric impedances oppositelyconnected between the same points in said circuit, means for impressinga high frequency electrometive force upon said circuit, and means fortransmitting to a work circuit, the energy of the resultinghiglifrequency current flowing through said impedances in said circuit. 11.The method of-signaling comprising causing a high frequency current totraverse a constantly active, symmetrically conducting thermionicimpedance, varying the value of said current by varying the magnitude ofsaid impedance in signals, and transmittingtheenergy of said .variedcurrent. I f i 1 12. A source of high frequency electrometive force, 'acircuit upon which substantially all of said electroinotive force ,isimpressed, a modulator comprisingltwo constantly operative. asymmetricconductors connected in opposition in branches of said circuit, an

accordance with element in said circuit fOfllljlllZlIlg current therein,substantially all of the current" m- ..cluce(l in said circuit by saidelectromotive [force passing through said element and sai modulator, andsignaling means controlling said modulator. a

13. In combination, means for supplying a high frequency electro-motiveforce, con- Ystantly active thermionic discharge means for symmetricallyconducting electrical energy, a translating element and means connectingsaid electro-motiveforce supply means, said discharge means and saidtranslating element in a series circuit.

14. In combination, means for supplying a high frequency current, animpedance device comprising two'constantly active asymmetric impedances'having the. terminals of the one respectively connected to unliketerminals of the other, .a translating element and means connecting saidhigh frequency current supply means, said impedance device and saidtranslating element in a series circuit.

l5. In a series circuit, symmetrically conducting means for permittingelectrical energy to pass only by electron discharge, means forimpressing an alternating electromotive force upon said circuit, meansfor varying the impedance of said conducting means substantiallyproportionally to the individual variations of speech currents,

and means for transmitting to a distant .oass by electron dischar emeans for impressing a. high frequency electro-motive force upon saidcircuit, and means for varying the impedance of said conducting means inaccordance with control currents.

17. In a series circuit, constantly active electron discharge means forsymmetrically conducting electrical energy, means for im pressing a highfrequency electro-motive force .upon said circuit, means for controllingtheimpedance of said electron discharge means, and means fortransmitting to a distant point the energy of the current traversingsaid electron discharge means.

18. In combination, a circuit, means for impressing a high frequencyelectro-motive force upon said circuit, a constantlyactive symmetricallygconduct-ing {thermionic impedance in series With said means, means forvarying the magnitude of said impedance in accordance with controlcurrents, and

means for transmitting the energy of the resulting current.

19. A circuit including a constantly active symmetrically conductingthermionic impedance, means in series with said impedance for impressinga high frequency electro-motive force upon said circuit,means forcontrolling the value of-said impedance in accordance with signals, andmeans for transmitting to a distant point the energy of t 1e currenttraversing said impedance.

In Witnesswhereof, I hereunto subscribe my name this fifteenth day ofSeptember RAYMOND A. YHEISING.

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